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Beginner

Scientific Name
Botrytis cinerea

Identification

• Flower petals infected with Botrytis turn brown as the disease progresses on the blossoms.
• Brown lesions form on the calyx and fruit and produce a grey-white fungal growth.
• A mass of grey, powdery mould eventually covers the surface of the infected tissue.
• Infected berries eventually become dried and mummified.

Often Confused With
Anthracnose Fruit Rot
Leather Rot

Period of Activity
Strawberry plants are susceptible to Botrytis during bloom and again as the fruits ripen.  Infection increases with moderate temperatures (15- 20°C or 59- 68°F) and high relative humidity and surface wetness during flowering.

Scouting Notes
Check for browning on blossoms and calyces of developing fruit.  As the fruit ripens, check for signs of rot.  Look in the center of rows where relative humidity is highest.  Older plantings where crop debris have built up over time are more at risk.  Blossoms injured by frost are highly susceptible to Botrytis infection.

Thresholds
None established.

Advanced

Scientific Name
Botrytis cinerea

Botrytis grey mould is the most destructive and widespread disease of strawberries in Ontario.  Symptoms of grey mould can develop pre-harvest and also in harvested fruit.

Identification
Flower petals infected with Botrytis turn brown as the disease progresses on the blossoms.  Brown lesions form on the calyx and fruit.  The lesions produce a grey-white fungal growth.  A mass of grey, powdery mould eventually covers the surface of the infected tissue.  Infected berries eventually become dried and mummified.  Botrytis occasionally infects crowns in cold storage.

Often Confused With
Anthracnose (Anthracnose has distinctly round lesions present anywhere on the fruit, with orange-brown-black spore masses and is never fluffy.)
Leather Rot  (Leather rot lesions are indistinct and associated with a foul smell.)

(Botrytis lesions are usually associated with the calyx, and covered in fluffy grey-beige spores.)

Biology
Botrytis grey mould is caused by the fungus Botrytis cinerea.  Dead strawberry leaves are the major source of spores that infect the flowers and fruit in spring.  Botrytis spores are dispersed by wind or splashing water.  Young blossom buds and open strawberry flowers are highly susceptible to infection from these spores.  Fruit infections usually remain dormant in immature fruit then become aggressive as the fruits ripen.  This latent infection is why many berries with no disease symptoms at harvest develop rot in storage.

Where Botrytis is sporulating in the field, the surface of many strawberries is likely contaminated by Botrytis spores before harvest.  Secondary infection can subsequently occur through microscopic wounds on the fruit at the post-harvest stages.  Spores germinate and infect strawberries between 0°C and 26°C (32- 79°F); the optimal temperature is 20°C (68°F).  They need water to germinate and require a period of wetness that varies with temperature.

Period of Activity
Strawberry plants are susceptible to Botrytis during bloom and again as the fruits ripen.  Infection increases with moderate temperatures (15- 20°C or 59- 68°F), high relative humidity and surface wetness during flowering.  Incidence is highly correlated with the amount of rainfall 11- 30 days prior to first harvest.

Scouting Notes
Check for browning on blossoms and calyces of developing fruit.  As the fruit ripens, check for signs of rot.  Look in the center of rows where relative humidity is highest.  Older plantings where crop debris have built up over time are more at risk.  Blossoms injured by frost are highly susceptible to Botrytis infection.

Thresholds
There are no thresholds for this disease.

Management Notes

• Choose crop management practices that keep rows narrow and encourage air flow in the row.
• Avoid excessive use of nitrogen, as lush growth is more susceptible to infection, and vigorously growing leaf canopies are slower to dry after wetting events.
• Apply fungicides during bloom.
• Till crop debris into the soil after renovation.
• All strawberry varieties are susceptible to Botrytis but some more than others; susceptible cultivars include Annapolis, Kent, Glooscap, Micmac, Sable and Redcoat.